Current disk files or direct access storage devices (DASD) are susceptible to chemically-induced failure. Organic vapors and corrodents may damage DASD performance. Organic vapors induce stiction at the interface between magnetic heads and disks. Corrodents can damage read/write heads and induce errors in thin film disks.
The copending application, U.S. Ser. No. 07/445,818, filed Dec. 4, 1989, now U.S. Pat. No. 5,030,260 granted Jul. 9, 1991 assigned to the assignee of the present invention, discloses a breather filter for a magnetic recording direct access storage device. The breather filter is mounted in a breather opening in an otherwise sealed (except for leaks) head/disk housing. The opening permits pressure within the housing to equalize with that of the ambient environment as pressure within the housing changes during start-up, operation, and shut down.
The breather filter as disclosed in this cited copending application comprises a prefilter medium for trapping particulate pollutants, one chemical filter medium of activated carbon fabric to trap undesired organic gases, a separate optional chemical filter medium to trap undesired inorganic gases, and a high efficiency particulate air (HEPA) final filter to trap particulate matter.
The application suggests that alternatively the particulate prefilter can be treated to trap inorganic gaseous pollutants. This in fact has been done in IBM DASD devices now on the market, wherein a fiberglass filter medium was treated with sodium carbonate to remove hydrogen chloride for preventing corrosion of Permalloy poletips in the read/write heads. At high humidity this treated fiberglass prefilter offers good protection against atmospheric sulfur dioxide but relatively poor protection against nitrogen dioxide and hydrogen sulfide. Also, the pressure drop through this treated fiberglass filter is relatively high, resulting in a correspondingly high pressure drop across the composite breather filter assembly. Prior to this invention, only particulate filter media of fiberglass were found to be treatable to provide protection against inorganic gaseous pollutants.
The Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 16, Third Edition, published by John Wiley & Sons, Inc., at pp. 125-138 has a section entitled "Novoloid Fibers". At pp. 136-137 there is described a novoloid-based activated carbon fiber (hereinafter "activated carbon fiber" which is formed by a one-step process combining both carbonization and activation, in an oxygen-free atmosphere containing steam and/or CO.sub.2 at about 900.degree. C. Pore radius distribution shows a single peak at about 1.5-1.8 nm (15-18 Angstroms, and thus a pore diameter of 30-36 Angstroms). As noted in the above-cited copending application, activated carbon fiber has been used as a filter medium to remove organic pollutants. However, there is no suggestion or teaching that activated carbon fibers could be treated with a chemical that in combination with the activated carbon provides a filter medium that removes both organic and inorganic gaseous or vapor pollutants.
The above constitutes the most pertinent prior art of which applicants are aware.
Of incidental interest is U.S. Pat. No. 4,684,510 which discloses a chemical breather filter for a magnetic storage device. The filter comprises a charcoal layer incorporated in a polyester or polyurethane foam to trap organic contaminants, one or more metal layers (such as copper or nickel mesh) to remove inorganic pollutants, and a particle-removing layer.
It is important that the pressure drop across the breather filter assembly be as low as possible so that any air drawn into the head/disk assembly housing will be drawn in through the breather filter and flow out through leak points (if any). As the pressure drop across the filter assembly increases, there is an increased likelihood that other leak paths into the interior of the housing via a gasket or other seal can permit contaminated air to be drawn into the housing in bypass of the filter.
There is a need for an improved inexpensive, single medium filter of reduced size which (a) prevents exposure of a device to both organic and inorganic chemical contaminants, (b) provides superior low humidity performance against corrosive gases, (c) eliminates the need for sodium carbonate-treated fiberglass filter media, and (d) provides corrosive protection with a significantly lower pressure drop than heretofore possible.